The present invention relates generally to pumps, particularly to pumps which do not force the fluid being pumped into a small gap between moving, sliding and/or rubbing structural pump surfaces inside the pump, and specifically to centrifugal pumps not requiring or using conventional rotating shaft seals or bearings in the pumped fluid.
Virtually all pumps, since the beginning of time, have had a "fundamental flaw", which causes most of the major pump problems. The "fundamental flaw" is that the fluid being pumped has always been forced into the small gap between some moving, sliding, and/or rubbing structural pump surfaces inside the pump, whether the pump is of the centrifugal or positive displacement type. This often causes serious problems for the pump operator.
Specifically, the primary cause of centrifugal pump failures is the failure of the rotating drive shaft seal. The shaft seal is necessary to seal the area where the rotating drive shaft enters the pressurized pump case. All rotating shaft seals operate in the same way, with the same fundamental flaw. All rotating shaft seals try to slide a moving seal surface very tightly against a stationary seal surface, so that fluid can not leak through the small gap between the moving and stationary surfaces. But there is always at least a microscopic gap between the seal surfaces where fluid can leak through. Sometimes the leaks become very large.
The U.S. Environmental Protection Agency has determined that the average chemical pump leaks 1000 pounds (375 kilograms) per year through "average" rotating shaft seals. Industrial quality pumps have their mechanical shaft seals fail every 89 days on average. Even the best medical quality centrifugal blood pumps have their shaft seals fail within 30 days.
Magnetic drive pumps were developed to eliminate the leaky, sliding surfaces of the rotating shaft seal. The sliding surfaces in the pumped fluid were not eliminated but were simply moved to a new location as the internal rotor support bearings. Problems with the internal sliding bearing surfaces include an inability to run dry for any length of time, any abrasives in the pumped fluid will wear out the bearings, and attempting to pump a fragile fluid such as blood will cause unacceptable damage because the blood cells will be destroyed by the grinding action of the sliding bearing surfaces. The magnetic drive pump is now the only "sealless" centrifugal pump design which is commercially available, but its high cost and unsatisfactory operating characteristics have limited its usefulness.
Magnetic bearings are sometimes used in place of sliding bearings to support the rotor in pumps including magnetic drive pumps. Magnetic bearing pumps will continue to have the fundamental flaw of all conventional pumps. The magnetic bearings will require a "close moving clearance" within the pumped fluid. Magnetic bearing pumps are inherently complicated, expensive, heavier, and inefficient, with a lower bearing load capacity than other conventional pumps.
Positive displacement pumps operate by mechanically forcing the pumped fluid from the low pressure zone to a high pressure zone and require some kind of sliding and/or moving surface to function as a valve to prevent fluid backflow. The valve can clog or can be damaged by abrasives in the fluid, or the valve can damage fragile fluids such as blood.
It can then be appreciated that previous attempts to correct the fundamental flaw only succeeded in relocating the sliding pump surface to a different place within the pumped fluid, which never really corrected the problem. Pump operators have always wanted to completely eliminate this fundamental flaw that causes so many pump problems, but no one else has ever been able to do so.
Thus, a need exists in the field of fluid pumping for completely eliminating the moving, sliding, and/or rubbing pump surfaces within the pumping chamber to provide many operating benefits. Further, a need exists for pumps which can be manufactured at a lower cost than conventional pumps.